1. Field of the Invention (Technical Field)
The invention relates to a system for determining the position and orientation of an object and more particularly a method and apparatus for an acoustic based determination of an arbitrary position and orientation of an object in space without any physical tether or connection to the object and with no alignments or predetermined spatial relationships between the system and the target object.
2. Background Art
The problem that this invention solves is efficient and accurate initial laying of an indirect fire weapon system for location and direction and subsequent attitude measurements necessary to firing the weapon system accurately at a target. Additionally, minimizing weight and power requirements as well as minimizing hardware physically attached to the weapon is crucial to the solution.
There are two methods that try to solve the problem. The first is the method employed by self-propelled weapon systems. Self propelled weapon systems use a three-axis attitude sensor and global positioning system (GPS) to determine pointing data. The second is a theoretical optical method. In this system, a barcode is attached to the end of the tube, and a barcode reader is used to measure the tube displacement and calculate azimuth.
Towed or man portable, indirect fire weapon systems are laid using a surveyed aiming circle. Once they are laid on an azimuth of fire, and have accurate position, all further aiming is done using optical sights and aiming references (aiming poles, collimators, or distant aiming points). There are several problems with this system/method of laying and subsequent pointing of indirect fire weapons; currently, survey is required to accurately emplace a mortar. An accurate survey is difficult to transfer to places where indirect fire weapon systems are set up. Additionally, the time it takes to emplace using an aiming circle is considered too long. With an aiming circle the location where the weapon is place is limited to a direct line of sight to the aiming circle. As a result, the weapon is not placed optimally for tactical considerations. While the use of an attitude sensor and GPS eliminates the need for a survey, this method also has shortcomings. The primary shortcomings of the self-propelled pointing system are excess weight, and power requirements. A towed or man portable solution cannot accommodate the equipment used on the self-propelled system. Additionally, the self propelled system is exposed to severe shock, vibration, and temperature, since it is mounted on the tube. This results in unacceptable failure rates of electronic components.
The second method is a system using optics to perform weapon pointing. A barcode is attached to the end of the weapon""s tube with a barcode reader placed a few meters away. As the tube is moved, the barcode reader picks up the displacement and performs the calculations to determine azimuth and elevation. Because this optical solution is theoretical, the accuracy requirements have not been proven.
The current methods fail to address weight, power, accuracy, and off tube mounting requirements.
All state of the art pointing systems require some type of position and attitude measurement device, such as a global positioning system (GPS) receiver and inertial navigation system (INS). The current method for solving this problem most often relies on installation of an Inertial Navigation System (gyroscopes and accelerometers) on the object of interest. For many applications this solution is prohibitively expensive. An optical approach requires exact positioning and re-alignments should the object""s position change. Standard ultrasonic techniques demand separate sensing modules for full three-dimensional determination of orientation. A radio frequency solution requires extremely fast detection electronics (rough calculations indicate such a system would need to resolve 4.6 picoseconds to sense the minimum incremental motion of a mortar tube).
There are several other prior art systems that attempt to solve the orientation and position determination problem as discussed above.
U.S. Pat. No. 4,853,863 to Cohen, et al., discloses a system that uses light, ultrasound and string wound on encoded, spring-loaded reels as mechanisms for calculations based on distances, angle measurements and doppler shift measurements (derivatives) which are then integrated to yield distance measurements. The Cohen, et al., system calls for 3 emitters and 3 detectors, all non-collinear for obtaining the measurements. The present invention utilizes 2 emitters (collinear) and 3 detectors (non-collinear). Another distinction from Cohen, et al., is that the present invention utilizes 6 distances coupled with a means of locating the system reference frame on the geodetic grid and a means of determining reference frame orientation to calculate absolute attitude and position. No such enhancement is to be found in Cohen, et al. In addition, Cohen, et al., does not reference fire control applications as disclosed herein.
U.S. Pat. No. 5,280,457 to Figueroa, et al., discloses a means for making absolute distance measurements using ultrasound and a xe2x80x9cstrobexe2x80x9d signal. The device is designed to eliminate the speed of sound as a system variable. Figueroa, et al., describes a means to locate a single point in 3-space, unlike the present invention which determines object position and orientation (6 degrees of freedom) in 3-space. Figueroa, et al., also describes, as a means to accomplish this, the use of one emitter and m+2 detectors to operate in m dimensions, i.e. one emitter and 5 detectors for a 3D system. Again, this is in contrast to the present invention, which uses 2 and 3 respectively. And finally, no application other than a self-calibrating means of locating a point is given Figueroa et al.
The present system provides an easy to use means of making accurate determinations of an object""s position and orientation. The object of interest can have an arbitrary orientation with respect to the sensing device. The user does not need to establish precise references or datum points when using the system.
The Remote Attitude and Position Indicating Device (RAPID) is a system for determining the location and pointing attitude of an object relative to a known coordinate system. The RAPID system uses an ultrasonic based measurement technique to determine the distances from two points on the object of interest to at least three points forming a plane in the known coordinate system. The derivation of the minimum six distances is accomplished by transmitting a distinct acoustic signal from each of two emitters and deriving the time of flight of each distinct signal from the two detectors to at least three detectors. Measurement of time of flight (TOF) relies on the fact that the acoustic signals travel at the speed of sound. Derivation of the minimum, six TOF measurements requires that the detection algorithm (hardware and/or software) ascertain the instant when the acoustic signals were sent. This can be accomplished using an RF pulse transmission, which occurs at the same time as the acoustic pulse but is received instantaneously at the detector and its associated receiver electronics. Similar results can be obtained without a reference pulse by measuring the round trip time of flight, where three acoustic signals are transmitted to the two object transducers, conditioned and returned to the transmitting transducer after a fixed delay. Upon derivation of the minimum, six TOF values, six emitter/pair distances are computed, for use in final computation of object orientation using standard geometric equations.
The method described above is implemented via two primary electronic assemblies. These consist of an emitter assembly and detector assembly. Note that there are two emitter assemblies on the object of interest. The emitter assembly contains the electronic circuitry necessary to generate the required drive signals for an acoustic emitter and the RF transceiver (in the case of the RF reference system). The detector assembly contains the electronic circuitry necessary to receive, amplify and process the signals detected by a minimum of three transducers. This circuitry may also include a RF transceiver for receipt of the xe2x80x9ctime sentxe2x80x9d reference signal. In the round trip measurement implementation, the detector assembly would contain the electronics necessary to drive the dual purpose transducers, and then receive, amplify and process the returned signals. The detector assembly will accommodate an interface to a attitude and heading reference device to enable calculation of object orientation in a know coordinate system (earth frame).
A primary object of the present invention is to enable automation of mortar laying, targeting and displacement.
Another object of the present invention is to enhance the lethality of the mortar platform.
Another object of the present invention is to connect the mortar to the digital battlefield.
A primary advantage of the present invention is that the system is minimally obtrusive to the weapons platform.
Another advantage of the present invention is since the primary electronics are not on the weapon, the environment is much more friendly, thereby reducing cost impacts of the environmental design requirements on the system
Yet another advantage of the present invention is that the system is extremely light, further supporting its inclusion as part of the manpack and towed mortar systems
Another advantage of the present invention is that the system does not require special setup or calibration, thereby improving operations and survivability
Another advantage of the present invention is that the system accuracy is dependent on the accuracy of the pitch/roll/heading system, thereby offering tailorable performance and cost.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.